1. Field of the Invention
The invention relates to the field of non-aqueous active metal electrochemical cells and, more particularly, to chemically inert, non-conducting high strength polymeric enclosures for such cells.
2. Description of the Prior Art
Much work has been done in the field of high energy battery systems utilizing highly reactive anode materials such as alkali metals in combination with non-aqueous electrolytes. Generally, such electrolytes normally consist of a solute which is commonly a metal salt or complex metal salt of the anode metal, i.e., of group I-A, II-A or III-A elements of the Periodic Table, dissolved in a compatible non-aqueous solvent. Batteries, often comprised of a group of such cells, are used in applications which require them to provide a high output over a wide temperature range. The most widely used electrochemical system of such cells consists of a lithium anode, a salt of a cation of the lithium anode such as lithium aluminum chloride (LiAlCl.sub.4) in a suitable solvent depolarizer such as thionyl chloride (SOCl.sub.2) or sulfuryl chloride (SO.sub.2 Cl.sub.2). The cathode is normally of carbon or a relatively inert carbonaceous material.
The highly reactive nature of the materials used in these cells has made it necessary to house the individual electrochemical cells in metal containers. The highly corrosive nature of these electrochemical materials has made it necessary for this metal to be stainless steel. Because of the possibility of high pressure build up in these cells under certain conditions, it is common practice to use a safety vent device welded into the metal cell case which allows gases and the electrolyte to be vented from the cell in a controlled manner in the event a predetermined pressure is exceeded.
In addition, the individual cells have heretofore required a glass-to-metal or ceramic-to-metal seal to effect electrical isolation of the primary lead. In lithium electrochemical cells, because of the high cell potential, the resistance of the glass or ceramic materials to electrochemcial and chemical corrosion has, in certain cases, been questionable with respect to extended periods of storability. In addition, to insure complete electrical isolation, potting techiques have commonly been used to isolate the battery "stack" of cells from the battery housing. This commonly interferes with the operation of the cell vent unless special design features are accommodated. Also, in the event of an electrochemical leakage from one or more of the cells of the battery, intercell current leakage can be established and cause battery self-discharge and even can create a safety hazard.
Thus, while cell electrochemistry has evolved and progressed relatively rapidly, cell enclosure technology has lagged behind. There has existed a definite need for a less expensive, chemically inert, strong, electrically insulating containing system for such cells which is less difficult to manufacture.